In general, halogen-based flame retardant agents, phosphorous flame retardant agents, inorganic flame retardant agents, etc. are used as polyurea flame retardant coating agents. Thereamong, halogen-based flame retardant agents as most generally used agents have an advantage of low costs. However, halogen-based flame retardant agents emit a large amount of toxic gases upon combustion and the halogen-based flame retardant agents are harmful to workers and the environment per se.
It is known that phosphorous flame retardants have 2 to 4 times higher flame retardant effects than halogen-based flame retardant coating agents, i.e., flame retardant coating agents to which a bromo or chloro group is introduced. However, since phosphorous is also an organic element, toxic gas reduction effects of phosphorous flame retardants are slight under ignition and direct heating conditions with maximum flame (1200□ or more) of a butane gas torch.
In the case of inorganic agents, flame retardant effects are somewhat exhibited at 600° C. or less, but are not almost exhibited at an ultrahigh temperature above 600□. In order to exhibit sufficient flame retardancy at 600° C. or more, the inorganic agents should be applied in an amount of 70% or more based on total solids when applied to coating agents. Accordingly, it is impossible to apply the inorganic agents to a working process.
In patent WO2009/121821A, flame retardancy of expanded graphite is used. Particularly, a thermoplastic molding composition or a foamed molding composition, such as polyethylene (PE), polypropylene (PP), or polyvinyl chloride (PVC), containing expandable graphite or a fluorine-containing polymer (e.g., fluorinated ethylene), as a flame retardant, represented by Formula 1 below is disclosed.

In addition, Korean Patent Laid-Open Publication No. 10-2006-0069721 relates to a method of preparing flame retardant polystyrene foam resin particles having inflammability. In particular, a method of imparting inflammability through formation of porous char (carbonized core) in the combustion by coating foamed polystyrene resin particles with expanded graphite particles, which have a layered crystalline structure and are expended 20 to 350 fold in size when heated, is disclosed.
However, the use of such known flame retardants is still inconvenient, or other properties as well as flame retardancy should still be enhanced.
The above information disclosed in this background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.